Abstract
Rupture of the scapholunate interosseous ligament can cause the dissociation of scaphoid and lunate bones, resulting in impaired wrist function. Current treatments (e.g., tendon-based surgical reconstruction, screw-based fixation, fusion, or carpectomy) may restore wrist stability, but do not address regeneration of the ruptured ligament, and may result in wrist functional limitations and osteoarthritis. Recently a novel multiphasic bone-ligament-bone scaffold was proposed, which aims to reconstruct the ruptured ligament, and which can be 3D-printed using medical-grade polycaprolactone. This scaffold is composed of a central ligament-scaffold section and features a bone attachment terminal at either end. Since the ligament-scaffold is the primary load bearing structure during physiological wrist motion, its geometry, mechanical properties, and the surgical placement of the scaffold are critical for performance optimisation. This study presents a patient-specific computational biomechanical evaluation of the effect of scaffold length, and positioning of the bone attachment sites. Through segmentation and image processing of medical image data for natural wrist motion, detailed 3D geometries as well as patient-specific physiological wrist motion could be derived. This data formed the input for detailed finite element analysis, enabling computational of scaffold stress and strain distributions, which are key predictors of scaffold structural integrity. The computational analysis demonstrated that longer scaffolds present reduced peak scaffold stresses and a more homogeneous stress state compared to shorter scaffolds. Furthermore, it was found that scaffolds attached at proximal sites experience lower stresses than those attached at distal sites. However, scaffold length, rather than bone terminal location, most strongly influences peak stress. For each scaffold terminal placement configuration, a basic metric was computed indicative of bone fracture risk. This metric was the minimum distance from the bone surface to the internal scaffold bone terminal. Analysis of this minimum bone thickness data confirmed further optimisation of terminal locations is warranted.
Highlights
The human wrist is a complex joint that includes 8 small carpal bones arranged in two rows (Fig 1)
This study presents a computational framework for the creation of personalised ligamentscaffold and associated surgical plan using finite element analysis (FEA)
The latter is derived from numerical fitting of the constitutive model to experimental mechanical data using inverse FEA
Summary
The human wrist is a complex joint that includes 8 small carpal bones arranged in two rows (Fig 1). The carpals are interconnected by intrinsic and extrinsic ligaments, and form at least 18 articulations. The scaphoid bone straddles both carpal rows and is bound to the lunate bone by the strong scapholunate interosseous ligament (SLIL). The SLIL is C-shaped and attached to the proximal edges of the scapholunate articulation (Fig 1, top right). The SLIL is comprised of three distinct anatomical regions, i.e. the dorsal, proximal, and volar region [1], which each presents distinct and anisotropic mechanical properties. The thickest and strongest of the three is the dorsal region, which is the primary stabiliser of the scapholunate joint [1–4], and is mostly commonly injured during violent hyperextension of the wrist, such as during a fall [5]
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